Release 1494
This adds the new Creation Channel model support to the TTA API, as well as being backwards-compatible for older API clients. Tested locally.
- adds models for the Creation Channel Creation entity
- adds picklist API endpoints for Creation Channel Services, Activities and Sources
- adds optional parameters for the Teacher Training Adviser endpoint /api/teacher_training_adviser/candidates
https://trello.com/c/msbZBxnU/7073-update-git-api-to-support-new-creation-channel-structure-e11-gc3